[JFFS2] fix race condition in jffs2_lzo_compress()

deflate_mutex protects the globals lzo_mem and lzo_compress_buf. However,
jffs2_lzo_compress() unlocks deflate_mutex _before_ it has copied out the
compressed data from lzo_compress_buf. Correct this by moving the mutex
unlock after the copy.

In addition, document what deflate_mutex actually protects.

Cc: [e-mail]
Signed-off-by: Geert Uytterhoeven <[e-mail]>
Acked-by: Richard Purdie <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

fs/jffs2/compr_lzo.c

···
 
 static void *lzo_mem;
 static void *lzo_compress_buf;
-static DEFINE_MUTEX(deflate_mutex);
+static DEFINE_MUTEX(deflate_mutex);	/* for lzo_mem and lzo_compress_buf */
 
 static void free_workspace(void)
 {
···
 
 	mutex_lock(&deflate_mutex);
 	ret = lzo1x_1_compress(data_in, *sourcelen, lzo_compress_buf, &compress_size, lzo_mem);
-	mutex_unlock(&deflate_mutex);
-
 	if (ret != LZO_E_OK)
-		return -1;
+		goto fail;
 
 	if (compress_size > *dstlen)
-		return -1;
+		goto fail;
 
 	memcpy(cpage_out, lzo_compress_buf, compress_size);
-	*dstlen = compress_size;
+	mutex_unlock(&deflate_mutex);
 
+	*dstlen = compress_size;
 	return 0;
+
+ fail:
+	mutex_unlock(&deflate_mutex);
+	return -1;
 }
 
 static int jffs2_lzo_decompress(unsigned char *data_in, unsigned char *cpage_out,